A high frequency heating apparatus having high frequency generating means for outputting high frequency waves to the inside of a heating chamber in which a heating target is accommodated has rapidly propagated as a microwave oven serving as cooking equipment for foodstuff, etc. because it can efficiently heat a heating target in a heating chamber in a short time. However, use of only heating based on high frequency heating has such a disadvantage that the cooking variations are limited.
Therefore, as conventional high frequency heating apparatuses have been provided a microwave oven having a high frequency wave generating apparatus for heating, a combination cooking range added with a convection heater for making a microwave oven generate hot air, etc. Furthermore, a steamer for introducing steam into the heating chamber to heat, a steam convection oven achieved by adding a steamer with a convection heater, etc. have been used as cooking devices.
When foodstuff is cooked by using a cooking device as described above, the cooling device is controlled so that the foodstuff has been cooked under the most excellent cooking state. That is, the cooking based on the combination of high frequency heating and hot air heating can be controlled by a combination cooking range, and the cooking based on the combination of steam heating and hot air heating can be controlled by a steam convection oven. However, the cooking based on the combination of high frequency heating and steam heating needs a labor of carrying out each of the heating treatments separately from each other while transferring heating target foodstuff between respective cooking devices. In order to overcome this disadvantage, a cooking device that can implement high frequency heating, steam heating and electric heating on its lone is known. This cooking device is disclosed in Patent Document 1, for example.
(Patent Document 1) JP-A-54-115448
According to this publication, a vaporizing chamber for generating heating steam is embedded at the lower side of the heating chamber, and water is supplied from a water tank with keeping a fixed water level at all times. Accordingly, it is difficult to carry out a daily cleaning work of the periphery of the heating chamber, and particularly in the vaporizing chamber, calcium, magnesium, etc. contained in water are condensed in the generating process of steam and precipitate and stick to the bottom portion of the vaporizing chamber and in pipes and thus the occurrence amount of steam is reduced, which causes such an unsanitary atmosphere that mold, etc. are liable to breed.
Furthermore, as a method of introducing steam into the heating chamber may be considered a system of generating steam by heating means such as a boiler or the like disposed at the outside of the heating chamber and supplying the steam thus generated into the heating chamber. However, there occur problems of breeding of miscellaneous bacteria in a pipe for introducing steam, breakage caused by freezing, contamination of foreign materials such as rust, etc., and it is frequently difficult to dismantle/clean the heating means. Therefore, the system of introducing steam from the outside is difficult to be adopted for cooking devices in which sanitation care is needed.
In many cases, a temperature sensor such as an infrared sensor or the like for measuring the temperature of a heating target is provided to a cooking device. In this case, when steam is fully filled in the heating chamber, the infrared sensor does not measure the temperature of the heating target, but measures the temperature of floated particles of steam existing between the heating target and the infrared sensor. Therefore, it is impossible to accurately measure the temperature of the heating target. In this case, heating control which is carried out on the basis of the temperature detection result of the infrared sensor is not normally operated, and thus a disadvantage such as insufficient heating, excessive heating or the like occurs. Particularly when automatic cooking is carried out according to a sequential procedure, the cooking process goes to a next step although heating fails, and the cooking target is irrecoverable by mere re-heating, standing to cool or the like, so that the cooking itself may finally fail.
Furthermore, heating cannot be necessarily performed according to a heating pattern having a high heating efficiency in accordance with the kind of the heating target and each temperature state of frozen articles, refrigerated articles or the like, and thus the heating time is lengthened.
Therefore, in consideration of the above situation, the applicant of this application has developed, as a prior invention, a high frequency heating apparatus having a steam generating function in which a steam generating portion can be easily cleaned and kept sanitary at all times, the temperature of a heating target can be accurately measured to carry out a proper heating treatment, and also the heating efficiency can be increased (see Patent Document 2).
(Patent Document 2) Japanese Patent Application No. 2002-216875 (Equivalent to WO 0307764)
FIGS. 1 to 7 show a high frequency heating apparatus having a steam generating function equipped with a steam generator according to the prior invention of the application of this application.
FIG. 1 is a front view showing the state that an opening/closing door of the high frequency heating apparatus is opened, FIG. 2 is a perspective view showing an evaporation tray of a steam generator used for this apparatus, FIG. 2 is a perspective view showing an evaporation tray heating heater and a reflection plate of the steam generator, and FIG. 4 is a cross-sectional view showing the steam generator.
The high frequency heating apparatus 60 having the steam generating function is a cooling device for supplying at least one of high frequency waves (microwave) and steam to a heating chamber 62 in which a heating target is accommodated, thereby cooking the heating target, and it comprises a magnetron 70 serving as the high frequency generator for generating high frequency waves, a steam generator 69 for generating steam in the heating chamber 62, a circulating fan 64 for stirring and circulating air in the heating chamber 62, a convection heater 66 serving as an indoor air heating heater for heating air circulated in the heating chamber 62, and an infrared sensor 63 for detecting the temperature in the heating chamber 62 through a detection hole formed in the wall surface of the heating chamber 62.
The heating chamber 62 is formed in the box-shaped main body case 61 which is opened at the front side thereof, and an opening/closing door 71 having a light transmissible window 71a for opening/closing the heating target take-out port of the heating chamber 62 is provided to the front side of the main body case 61. The opening/closing door 71 is joined to the lower edge of the main body case 61 at the lower end thereof through a hinge so that the opening/closing door 71 can be opened/closed in the vertical direction. A predetermined adiabatic space is secured between the wall surfaces of the heating chamber 62 and the main body case 61, and the space is filled with adiabatic material as occasion demands. Particularly, a space at the back side of the heating chamber 62 serves as a circulating fan room 67 in which the circulating fan 64 and a driving motor 84 (see FIG. 7) are accommodated, and the wall of the back surface of the heating chamber 62 serves as a partition plate 68 through which the heating chamber 62 and the circulating fan room 67 are compartmented. Air suction vent holes for sucking air from the heating chamber 62 side to the circulating fan room 67 side and air blowing vent holes 72 for blowing air from the circulating fan room 67 side to the heating chamber 62 side are formed in the partition plate 68 so that the formation areas thereof are discriminated from each other. The respective vent holes 65, 72 are formed as many punch holes.
The circulating fan 64 is disposed so that the rotational center thereof is located at the center portion of the rectangular partition plate 68, and a rectangular and annular convection heater 66 is provided in the circulating fan room 67 so as to surround the circulating fan 64. The air suction vent holes 65 formed in the partition plate 68 are disposed in front of the circulating fan 64, and the air blowing vent holes are disposed along the rectangular and annular convection heater 66. The circulating fan 64 is set so that air flows from the front side of the circulating fan 64 to the rear side thereof at which the driving motor 84 is located when the circulating fan 64 is rotated. Therefore, air in the heating chamber 62 is sucked through the air suction vent holes 65 to the center portion of the circulating fan 64, passed through the convection heater 66 in the circulating room 67 and then blown out from the air blowing vent holes 72 to the heating chamber 62. Accordingly, through this air flow, the air in the heating chamber 62 is circulated through the circulating fan 67 while stirred.
The magnetron 70 is disposed in a space below the heating chamber 62, for example, and a stirrer vane 73 is provided at a position where high frequency waves generated by the magnetron are received. The high frequency waves from the magnetron 70 are irradiated to the rotating stirrer vane 73, and the high frequency waves are supplied to the heating chamber 62 by the stirrer vane 73 while stirred. The location of the magnetron 70 and the stirrer vane 73 is not limited to the bottom portion of the heating chamber 62, but they may be located at the upper surface of the heating chamber 62 or at the side surface thereof.
As shown in FIG. 2, the steam generator 69 comprises an evaporation tray 75 having a water stocking recess place 75a for generating steam by heating, an evaporation tray heating heater 76 that is disposed at the lower side of the evaporation tray 75 and heats the evaporation tray 75, and a reflection plate 77 having a substantially U-shaped section for reflecting radiation heat of the heater to the evaporation tray 75. The evaporation tray 75 is formed of stainless and designed to have an slender plate shape, and it is disposed at the bottom surface of the back side opposite to the heating target take-out port of the heating chamber 62 and oriented so that the longitudinal direction thereof is along the partition plate 68. A glass tube heater, a sheathed heater, a plate heater or the like is usable as the evaporation tray heating heater 76.
FIG. 5 is a block diagram showing a control system for controlling the high frequency heating apparatus 60 having the steam generating function. This control system is mainly constructed by a controller 701 having a microprocessor, for example. The controller 701 mainly receives/transmits signals from/to a power supply portion 703, a storage portion 705, an input operating portion 707, a display panel 709, a heating portion 711, a cooling fan 81, etc.
The input operating portion 707 is connected to various operating switches such as a start switch 719 for instructing start of heating, a switching switch 721 for switching a heating method such as high frequency heating, steam heating, etc., an automatic cooking switch 723 for starting programs stored in advance, etc.
The heating portion 711 is connected to the high frequency generator 70, the steam generator 69, the circulating fan 64, the infrared sensor 63, etc. The high frequency generator 70 is operated in cooperation with a radio stirring portion (the driving portion of the stirrer vane) 73, and the steam generator 69 is connected to the evaporation tray heating heater 76, the indoor air heating heater 66 (convection heater), etc. Elements other than the mechanical constituent elements described above (for example, a water feeding pump 80, a door air blowing dumper 82, an exhaust dumper 83, etc.) are contained in this block diagram, however, this will be described by embodiments described later.
Next, the basic operation of the high frequency heating apparatus 60 having the steam generating function described above will be described with reference to the flowchart of FIG. 6.
As an operating procedure, foodstuff to be heated is put on a dish or the like and inserted into the heating chamber 62 and then the opening/closing door 71 is closed. The heating method, the heating temperature or time are set by the input operating portion 707 (step 10, subsequently will be abbreviated as S10), and the start switch is turned on (S11). At this time, the heating treatment is automatically carried out by the operation of the controller 701 (S12).
That is, the controller 701 reads out the heating temperature/time thus set, selects/executes the optimal cooking method on the basis of the heating temperature/time thus read out, and judges whether the heating temperature/time thus set is reached (S13). When it reaches the set value, each heating source is stopped and the heating treatment is finished (S14). In S12, generation of steam, the indoor air heating heater, the rotation of the circulating fan and the high frequency heating are individually or simultaneously carried out.
The operation carried out when a mode of “generating stream +turning on circulating fan”, for example, is selected/executed in the above-described operation will be described. When this mode is selected, the evaporation tray heating heater 76 is turned on to heat water of the evaporation tray 76, and thus steam S occurs as indicated in the diagram showing the operation of the high frequency heating apparatus 60 in FIG. 7. The steam S rising from the evaporation tray 75 is sucked from the air suction vent holes 65 provided substantially at the center portion of the partition plate 68 to the center portion of the circulating fan 64. Then, the steam S is passed through the circulating fan room 67, and blown out from the air blowing vent holes 72 provided to the peripheral portion of the partition plate 68 into the heating chamber 67. The steam thus blown out is stirred in the heating chamber 62, and sucked from the air suction vent holes 65 substantially at the center portion of the partition plate 68 to the circulating fan room 67 side again. Accordingly, a circulation path is formed between the inside of the heating chamber 62 and the circulating fan room 67. No air blowing vent hole 72 is provided below the location position of the circulating fan 64 of the partition plate 68, so that generated steam is introduced to the air suction vent holes 65. As indicated by outlined arrows in the figures, steam is circulated in the heating chamber 62, whereby the steam is sprayed to the heating target M.
At this time, by turning on the indoor air heating heater 66, the steam in the heating chamber 62 is heated, and thus the temperature of the steam circulated in the heating chamber 62 can be set to a high temperature. Accordingly, so-called overheated steam is achieved, and cooking can be carried out so that the surface of the heating target M gets burned. Furthermore, when high frequency heating is carried out, the magnetron 70 is turned on and the stirrer vane 73 is rotated, whereby high frequency waves are supplied into the heating chamber 62 while stirred and high frequency cooking can be uniformly performed.
As described above, according to the high frequency heating apparatus of the prior invention, steam is generated not at the outside of the heating chamber 62, but in the heating chamber 62. Therefore, the evaporation tray 75 on which steam occurs can be easily cleaned as in the case where the inside of the heating chamber 62 is cleaned. For example, in the process of occurrence of steam, calcium, magnesium, chlorine compound, etc. are condensed, and they precipitate and stick at the bottom portion of the evaporation tray 75. However, the materials adhering to the surface of the evaporation tray 75 can be cleanly removed by wiping out them with cloth or the like.
Furthermore, as described with reference to FIG. 4, the evaporation tray disposed in the high frequency heating apparatus is heated by radiation heat of the heater, and the radiation heat from the heater is reflected from the reflection plate to the evaporation tray, so that the heating efficiency is increased.
As described above, in the prior invention, the heating efficiency is more greatly enhanced than the conventional apparatus, and the maintenance thereof can be easily performed.
However, the applicant of this application has not yet been satisfied with the above invention, and has sought further increase of the heating efficiency. However, the reflection plate is bulky and it obstructs the trend of miniaturization, and the applicant considers that this is not used.
The present invention has an object to overcome these disadvantages, and provide a high frequency heating apparatus having a miniaturized steam generator in which when water is dropped, the dropped water can be remarkably speedily evaporated with even the same watt value.
Furthermore, the present invention has an object to provide a high frequency heating apparatus having a steam generating function in which a steam generator can be easily cleaned and keeps sanitary at all times, an optimal amount of steam is generated for foodstuff, miniaturization is implemented and the heating efficiency is increased.